How to return string that contains string/int variables

Question

For example, if I have this little function:

string lw(int a, int b) {    
    return "lw $" + a + "0($" + b + ")\n";
}

....and make the call lw(1,2) in my main function I want it to return "lw $1, 0($2)".

But I keep getting an error: invalid operands of types ‘const char*’ and ‘const char [11]’ to binary ‘operator+’

What am I doing wrong? I pretty much copied an example from class, and changed it to suit my function.

Answer 1

You are trying to concatenate integers to strings, and C++ can't convert values of such different types. Your best bet is to use std::ostringstream to construct the result string:

#include <sstream>

// ...

string lw(int a, int b)
{
    ostringstream os;
    os << "lw $" << a << "0($" << b << ")\n";
    return os.str();
}

If you have Boost, you can use Boost.Lexical_cast:

#include <boost/lexical_cast.hpp>

// ...

string lw(int a, int b)
{
    return
        string("lw $") +
        boost::lexical_cast<std::string>(a) +
        string("0($") +
        boost::lexical_cast<std::string>(b) +
        string(")\n");
}

---

And now with C++11 and later there is std::to_string:

string lw(int a, int b)
{
    return
        string("lw $") +
        std::to_string(a) +
        string("0($") +
        std::to_string(b) +
        string(")\n");
}

Answer 2

#include <sstream>

string lw(int a, int b) {    
    std::string s;
    std::stringstream out;
    out << "lw $" << a << "0($" << b << ")" << endl;
    s = out.str();
    return s;
}